This invention relates to a process for producing an extruded sheet of a thermoplastic resin material and to an apparatus for producing such a product.
The production of transparent thermoplastic sheets by an extrusion process is very well known in general terms and it is also known to add carefully controlled amounts of a dye or a pigment to confer on the sheet any desired hue. It is however somewhat more difficult to produce a transparent sheet with a gradient band of color therein. One specific end-use for which plastic sheets with such color bands are needed is in the production of interlayers for laminated car windshields. Such windshields usually comprise a layer of plasticized polyvinyl butyral [PVB] sandwiched between glass sheets. A popular option in an automobile is a windshield in which the upper region has a colored gradient band so as to reduce the intensity of the sunlight shining through that portion of the windshield and on to the driver and front seat passengers. This colored gradient band shades gradually down to the dominant hue of the rest of the windshield.
The present invention provides a means of producing a plastic sheet having a gradient color band and although its use is not so closely restricted, its main utility is in the production of a gradient color band in a PVB interlayer for an automobile windshield.